U.S. Pat. No. 3,743,015, which is owned by the same corporate entity which owns the subject invention, describes and claims a mud saver ball valve of the type discussed above. The teachings of this patent are totally incorporated by reference as if fully described herein. A normally closed ball element is rotated open by a piston which moves responsive to increased fluid pressure above the element and overcomes the force of one or more springs which hold the ball element closed. If when the mud supply pressure is cut off the pressure within the drill string is still abnormally high the valve will not close since the piston is exposed to the higher pressure.
U.S. Pat. No. 3,036,590 which is also owned by the same corporate entity which owns the subject invention, is directed to an earlier version of a manually operable, ball-type, kelly cock or safety valve.